This is generally in the area of non-invasive methods and apparatus for sampling of analytes present in body fluids, including sweat, such as glucose, heavy metals, and compounds of abuse.
The development of transdermal methods of delivering drugs through the skin has been made possible by the optimization of solvent conditions of individual drugs so that they solubilize and partition into the stratum corneum skin layer (Brown, L. and Langer, R., xe2x80x9cTransdermal Delivery of Drugs,xe2x80x9d Ann. Rev. Med. 39: 221-229, 1988). In addition, transdermal diffusion of drug compounds has been also enhanced using iontophoresis, electroporation and ultrasound. These observations have lead to the further investigation of using the transdermal route to detect metabolites in the skin. Virtually all of the work in the scientific literature has been focused in the area of glucose detection in the treatment of diabetes mellitus. However, large fluctuations in glucose concentrations can occur within minutes after the ingestion of a carbohydrate loaded meal. In contrast, glucose diffusion through the stratum corneum skin layer is relatively slow and lags behind these glycemic variations. Thus, there is a significant xe2x80x9clag timexe2x80x9d between the skin measurement of glucose concentration through the stratum corneum skin layer and the actual blood concentration.
Previous attempts restricted to the detection of glucose have not and can not be extended to heavy metals. A more useful and uninvestigated application of transdermal diffusion is to non-invasively detect analytes whose concentration does not vary significantly over short time periods. This is especially important for the detection of chemicals such as heavy metals. For example, a heavy metal such as lithium used to treat manic depressives could be detected by psychiatrists to easily determine patient compliance. The detection of iron would be useful for the detection of iron overload diseases.
Lead (Pb) is an example of a heavy metal which is also a toxic substance. Public health organizations in the United States require all children to be tested several times before beginning school and during their early education. It is required for kindergarten grade entry in many school districts in the United States. Studies indicate that nearly 10% of the children in the United States ages six and under, or 1.7 million children, are victims of lead poisoning (Carolina Environment, Inc. Aug. 8, 1996). The United States Public Health Service estimates one out of six children under the age of six has enough lead in their blood to place them in what scientists consider the risky zone. Childhood lead poisoning has no predilection for socioeconomics or geography.
Although adults are susceptible to lead poisoning, children remain at the highest risk due to the natural instinct to introduce non-food items into their bodies. The effects of lead poisoning include learning disabilities, delinquent behavior, hyperactivity, decreased growth, kidney and heart disease, and even brain damage. Common potential lead-contaminated areas include older play equipment and chipping paint from window and door trim, and even walls.
The symptoms of lead poisoning include headaches, irritability, abdominal pain, vomiting, anemia, weight loss, poor attention span, noticeable learning difficulty, slowed speech development, and hyperactivity. The effects of lead poisoning include reading and learning disabilities, speech and language handicaps, lowered I.Q., neurological deficits, behavior problems, mental retardation, kidney disease, heart disease, stroke, and death.
Current test procedures for lead are traumatic for young children as they require venipuncture and extraction of a blood sample. The scientific literature does not describe non-invasive methodologies for detecting heavy metals via the dermal route.
There are numerous descriptions of the toxicology of Pb absorbed through the skin and then found to result in toxic effects or elevated levels in other tissues. This is especially true in the use of lead for topical cosmetic applications (Moore et al., Food Cosmet. Toxicol. 18(4) :399-405(1980)) and in industrial applications (Hine et al., J. Occup. Med. 11(11):568-75 (1969)). In one citation in the scientific literature, sweat is used to assess the absorption of lead through the skin, but not from systemic blood supply and organs to the skin (Lilley et al., Science Total Environ. 76(2-3):267-78 (1988)).
Other examples of plasma heavy metal concentrations caused by skin absorption include zinc (Morgan et al., Br. J. Dermatol. 102(5):579-83 (1980)). Cadmium, chromium, and arsenic have also been detected in male reproductive organs (Danielsson et al., Arch. Toxicol. Suppl. 7:177-80 (1984)).
Sweat lead detection was well studied by an Australian group at CSIRO, Menai, Australia. Stauber and colleagues worked on sweat lead detection for occupational lead absorption through skin. They found that even inorganic lead can be absorbed through skin and rapidly distributed through the body (Stauber et al., Science Total Environ. 145:55-70 (1994)). In one of their experiments (Lilley et al., Science Total Environ. 76:267-278 (1988)), lead powder was placed on the left arm of a healthy adult male volunteer, and a certain region of skin of the right arm was induced to sweat for lead detection. The placing of 6 mg of lead as 0.5 M lead nitrate to the left arm resulted in the increase in lead concentration in pilocarpine-induced iontophoresis samples in the right arm. No changes were found in the blood or urine samples. However, Omokhodion and Crockford, Science Total Environ. 103:113-122 (1991)) found that there is a good relationship between blood and sweat lead levels among non-occupationally exposed persons.
Many other substances must be measured on a frequent basis, resulting in trauma and pain to the patient. Examples include measuring blood glucose in diabetics and sampling drugs of abuse in cocaine addicts. Efforts for the non-invasive detection of glucose have focused on transdermal extraction of glucose using solvents, iontophoresis or using the penetration of infrared light through the skin. None of these glucose efforts have been commercialized. Among the scientific difficulties associated with glucose detection are that glucose concentrations change transiently and quickly throughout the day, and often do so at rates which exceed the permeability rate of the glucose molecule through the skin. Therefore the iontophoretic or solvent extraction routes have proven to yield irreproducible data. The use of infrared light has been plagued with interference from other substances of similar structure found in vivo and the inability to calibrate these devices reproducibly.
Transdermal detection of substrates other than lead from sweat has been applied to non-invasive devices. Several transdermal alcohol detection devices have been developed by Dermal Systems International to detect alcohol from sweat (Swift, Addiction 88:1037-1039 (1993)). One of those methods is an alcohol dosimeter or xe2x80x9csweat patchxe2x80x9d which is a portable, wearable, non-invasive, occlusive patch applied to the skin surface. However, it requires a 7-10 day period for the detection. Another alcohol xe2x80x9cBand-Aid(copyright)xe2x80x9d is a small strip applied to the skin that utilized enzymatic calorimetric detection to estimate blood ethanol concentration over several minutes (Roizman et al., Anesthesiology 73(3A):A512, (1990)). However, estimating concentration of a drug (e.g. alcohol) across pharmacokinetic compartments (blood and skin) is not always straightforward. Sweat detection also involves the complexity of both passive diffusion through the skin (Scheuplein and Blank, Physiological Rev. 51(4):702-747 (1971)) and active secretion by eccrine glands, primarily sweat glands (Brusilow and Gordis, Amer. J. Dis. Child 112:328-333 (1966)).
xe2x80x9cBand-Aid(copyright)xe2x80x9d sweat patches have also been tested in a human clinical study to monitor drug use, for example with cocaine (Burns and Baselt, J. Analytical Toxicol. 19:41-48 (1995)). A cellulose based patch collected sweat in a seven day period and substantial cocaine concentrations were detected in the patches. However, quantitative interpretation was beyond the xe2x80x9ccapabilities of the technologyxe2x80x9d (Burns and Baselt, supra, at 45, col. 1). This sweat patch was developed by Sudormed, Inc., which was later acquired by Pacific Biometrics, Inc. (Lake Forest, Calif.).
xe2x80x9cReversexe2x80x9d transdermal detection has been used for glucose detection. Because of the non-polar property of the glucose molecule, the xe2x80x9creversexe2x80x9d transdermal glucose detection requires certain enhanced methods, such as iontophoresis and ultrasound. Studies of xe2x80x9creversexe2x80x9d transdermal detection has demonstrated some results for the detection of glucose in the presence of current (Glikfeld et al., Pharmaceutical Res. 6(11):988-990 (1989); Rao et al., Pharmaceutical Res. 10(12):1751-1755 (1993)). However, all of these methods require complex apparatus to extract the analytes.
It is therefore an object of the present invention to provide a method and apparatus for non-invasively obtaining samples of body fluids for testing for the presence and/or amount of a particular analyte in the body fluid, which is easy and inexpensive.
A method and apparatus for non-invasive extraction and/or detection of chemicals such as heavy metals and cocaine and analytes such as blood glucose have been developed. A patch or hydrogel containing a reagent such as N-methyl pyrrole, or a similar pyrrolidone or mixture thereof, is used to extract the chemical or analyte to be measured through the epidermis and/or hair. This method is useful for detecting analytes which are generally present in relatively constant blood concentrations. The method is particularly useful for the detection of heavy metals such as lead, lithium, copper, iron, and has been demonstrated to be useful to extract both drugs and metabolic analytes. In the preferred embodiment, the method involves the use of the water miscible solvent N-methyl pyrrolidone (NMP) in an aqueous solution which is incorporated into an adsorbent pad or hydrogel. This adsorbent pad is placed on the skin for a defined time period, removed and then analyzed for the substance of interest. Analytical means can also be incorporated as part of the adsorbent pad in order to conduct both the extraction of the chemical of interest and the assay in situ. Examples demonstrate measurement of lead, cocaine, glucose, and acetaminophen, demonstrating the very broad range of materials which can be extracted. Comparative examples demonstrate that the same results cannot be obtained using other reagents such as dimethylsulfoxide (DMSO).